Metal sealing glass composite with matched coefficients of thermal expansion

ABSTRACT

The present invention relates to a glass for making glass to metal seals. The coefficient of thermal expansion of the glass is in excess of 160×10 -7  in/in/°C. making the glass particularly useful for sealing copper and copper based alloys. The glass has particular utility in the manufacture of electronic packages and multi-layer circuitry.

This application is a division of application Ser. No. 169,635, filedMar. 17, 1988, now U.S. Pat. No. 4,952,531.

There are many metal-glass-ceramic applications and systems which havein common the bonding of a glass or ceramic material to the surface of ametal. One common application is in the manufacture of hermetic packagesdesigned to enclose electronic devices such as silicon semiconductordevices.

Perhaps the most common hermetic package is the ceramic dual in linepackage commonly known as the CERDIP. The package contains a basecomponent and a cover component made of aluminum oxide. The componentsare joined together, frequently with a metal leadframe disposed between,by a sealing glass. The glass is fabricated to have a coefficient ofthermal expansion approximating that of the aluminum oxide components,about 49×10⁻⁷ in/in/° C.

As semiconductor technology developed, the electronic devices becamemore complex. More electronic circuitry was positioned on smallersurface areas and as a result, the electronic device generated more heatduring operation. Aluminum oxide has fairly poor thermal conductivityand as a result, alternatives to the CERDIP were developed.

Among these alternatives was the metal package. A metal or metal alloyreplaced the aluminum oxide in forming the base and cover components ofthe package. Initially, low expansion alloys such as theiron-nickel-cobalt alloy known by the tradename KOVAR or low expansionmetals such as molybdenum were used. Sealing glasses used for sealingCERDIP packages were adapted to the metal packages. To increase adhesionof the glass to the metal components, a thin layer of a metal oxide wasformed on the surface of the base and cover components in accordancewith technology known from the fabrication of glass to metal seals forthe vacuum tube industry.

A glass suitable for bonding to molybdenum (coefficient of thermalexpansion=49×10⁻⁷ in/in/° C.) containing SiO₂, Al₂ O₃, MgO, ZrO₂, TiO₂and Li₂ O is disclosed in U.S. Pat. No. 3,473,999 to Mochow.

As the semiconductor devices continued to increase in complexity, theneed for package components with improved thermal conductivity alsoincreased. Typically, there is a correlation between thermalconductivity and coefficient of thermal expansion. As the thermalconductivity increases, the coefficient of thermal conductivity likewiseincreases. Therefore, the higher conductivity electronic packagesbrought about a need for sealing glasses with higher coefficients ofthermal expansion.

A sealing glass for stainless steel having a coefficient of thermalexpansion of 120×10⁻⁷ -140×10⁻⁷ in/in/° C. containing SiO₂, K₂ O, Na₂ O,Al₂ O₃ and MgO is disclosed in U.S. Pat. No. 3,804,703 to Hirayama.

A sealing glass for nickel having a coefficient of thermal expansion ofabout 150×10⁻⁷ in/in/° C. and containing SiO₂, Na₂ O K₂ O , a mixture of(BaO, SrO and CaO) and Al₂ O₃ is disclosed in U.S. Pat. No. 2,948,992 toOldfield. Yet another relatively high expansion glass is known by thetradename CORNING 1990 and sold by Corning Glass Works located inCorning, N.Y. This glass contains SiO₂, Li₂ O, Na₂ O , K₂ O and PbO andhas a coefficient of thermal expansion of about 136×10⁻⁷ in/in/° C.

To maximize thermal conductivity, fabrication of components forelectronic packages from copper or copper alloys is preferred. Thecoefficient of thermal expansion of these materials is in the range offrom 160×10⁻⁷ -180×10⁻⁷ in/in/° C. Glasses with coefficients of thermalexpansion in the same range were required. Glasses have been developedwhich are close to the coefficient of thermal expansion of copper. Forexample, U.S. Pat. No. 3,407,091 to Busdiecker discloses a glasscontaining Al₂ O₃, K₂ O, ZnO and P₂ O₅ for sealing to copper or copperalloys. The coefficient of thermal expansion of this glass was measuredto be 141×10⁻⁷ in/in/° C. However, if the mismatch between the glass andthe substrate is much greater than about 10%, it has been found theglass will develop microcracks and hermeticity of the package will belost.

Sealing glasses with coefficients of thermal expansion approximatingthat of copper have been made by adding a filler with a high coefficientof thermal expansion, such as calcium fluoride, to a sealing glass toachieve coefficients of thermal expansion about equal to that of copper.U.S. Pat. No. 4,185,139 to Smermos as well as U.S. Pat. Nos. 4,801,488to Smith, III and 4,752,521 to Smith, III et. al. disclose the use of afiller.

A problem with using a filler is excessive amounts of filler lead to adeterioration of the rheological properties that can affect sealintegrity. As the sealing glass is heated, some of the filler isdissolved. Dissolution of CaF₂, one known filler, can lead to outgassingresulting in the dispersion of fluorine ions throughout the glass. Thefluorine ions degrade the electrical resistivity and chemical durabilityof the glass. One approach to the problem of excessive dissolution iscoating the filler as shown in U.S. Pat. No. 4,185,139 to Smermos.However, coating is difficult and does not solve the problem ofexcessive filler.

Lead oxide is a common component in sealing glasses. The lead oxidelowers the melting point of the glass. This is advantageous in glassescontaining fillers as the lower the sealing temperature, the lessdissolution. However, the nature of lead glasses restrict their use inreducing atmospheres and neutral atmospheres which are sometimesessential to control the oxidation behavior of the copper alloys.

In accordance with the present invention, a sealing glass is providedwith a coefficient of thermal expansion approximately matching that ofcopper or copper based alloys, that is a coefficient of thermalexpansion in the range of from about 160×10⁻⁷ to about 180×10⁻⁷ in/in/°C. The sealing glass is essentially lead and fluorine free and containsSiO₂, Na₂ O, K₂ O, BaO and Al₂ O₃. The sealing glass is a homogeneousmixture of approximately the following ratio:

SiO₂ : at least about 50 molar percent

Na₂ O : from about 5 to about 30 molar percent

K₂ O : from about 5 to about 30 molar percent

BaO : from about 10 to about 20 molar percent

Al₂ O₃ : up to 5 molar percent

The glass is sealed at temperatures up to about 800° C. withoutdeterioration. High temperature stability permits the assembly of copperalloy packages which may be thermally treated subsequent to sealing. Ina preferred embodiment, the copper package is age hardened subsequent toglass sealing.

Accordingly, it is an object of the present invention to provide asealing glass which has a coefficient of thermal expansion approximatelyequal to that of copper or a copper based alloy.

It is a preferred feature of the invention that the glass is homogeneousand free of undissolved or partially dissolved fillers.

It is another feature of the invention that the glass is essentiallyfree of fluorine and lead.

It is a feature of the invention that the glass has a meltingtemperature of about 800° C. permitting thermal aging of the assembledpackage.

These and other advantages will become more apparent from the followingdescription and drawings.

FIG. 1 shows in cross section an electronic package manufactured inaccordance with the invention of this application.

FIG. 2 shows in cross section a glass-metal composite materialmanufactured in accordance with the invention of this application.

FIG. 3 shows in cross section a multi-layer circuit manufactured inaccordance with the invention of this application.

The invention relates to sealing glasses for hermetic metal packages.The glasses are characterized by a coefficient of thermal expansionapproximately matching a metal or metal alloy, preferably that of copperor a copper based alloy. More precisely, the coefficient of thermalexpansion of the glass is in excess of about 160×10⁻⁷ in/in/° C.Preferably, the coefficient of thermal expansion is in the range of fromabout 160×10⁻⁷ in/in/° C. to about 180×10⁻⁷ in/in/° C. and, mostpreferably, in the range of from about 165×10⁻⁷ in/in/° C. to about175×10⁻⁷ in/in/° C.

The glasses are further preferably homogeneous, that is, without anyundissolved fillers or other media present.

The glasses are preferably fluorine free and while lead oxide may beadded to adjust the melting point as discussed below, the concentrationof lead oxide is preferably low.

In a preferred composition, the glass contains SiO₂, BaO, a mixture ofNa₂ O and K₂ O, Al₂ O₃ and possibly an additive to give the sealingglass desired properties.

The glass is predominantly comprised of silicon dioxide, at least about50 molar percent. More preferably, the concentration of SiO₂ is fromabout 55 molar percent to about 65 molar percent and, most preferably,the concentration is from about 58 molar percent to about 60 molarpercent.

The barium oxide component is preferably present in concentrations offrom about ten molar percent to about twenty molar percent. It has beenfound that barium oxide is a major contributor to the thermal expansioncoefficient of the glass composite. The desired concentration of BaO isdetermined by the coefficient of thermal expansion of the metal alloywhich is being sealed. For most copper or copper based alloys, it hasbeen found that a BaO concentration of from about twelve to aboutfifteen molar percent is most preferred.

An alkaline oxide component is included. The alkaline oxide component ispreferably comprised of about equal molar concentrations of two alkalineoxides. The use of about equal molar concentrations of two alkalineoxides takes advantage of the "Mixed Alkali Effect". The "Mixed AlkaliEffect" predicts that the diffusion of alkali ions is drasticallyreduced when those alkali ions are present in equi-molar proportionsrather than a single alkali ion with the molar concentration of the sum.Lower diffusion rates will increase the electrical resistivity of thesealing glass, thereby isolating the leadframe from the electronicpackage components. As disclosed in U.S. Pat. No. 3,804,703 to Hirayama,the "Mixed Alkali Effect" also seems to improve the moisture resistanceof the glass and increase the coefficient of thermal expansion. Whileother alkali oxides may be used, namely the oxides of lithium, rubidiumand/or cesium, it has been found the maximum increase in coefficient ofthermal expansion is obtained with a mixture of Na₂ O and K₂ O.

The concentration of total alkaline oxide is preferably from abouttwenty molar percent to about thirty molar percent and, more preferably,from about 25 molar percent to about 28 molar percent. For example,about 14 molar percent Na₂ O and 14 molar percent K₂ O.

Preferably, a small amount of aluminum oxide is also added to the glass.It has been found that aluminum oxide increases the chemical resistanceof the glass. The aluminum oxide serves to lower the coefficient ofthermal expansion of the glass and, therefore, is preferably in aconcentration of up to about 5 molar percent and, more preferably, in aconcentration of from about 0.5 molar percent to about 3 molar percent.

Various other additives may be combined with the glass, generally inconcentrations of less than about 10 molar percent. For example, smallamounts of lead oxide will lower the melting point of the glass. Otheradditives which may be combined with the glass include, but are notlimited to Li₂ O, B₂ O₃, P₂ O₅, MgO, CaO, GeO₂ and SrO.

As an illustrative example, which is not intended to limit theinvention, the following glass composition has been found to give acoefficient of thermal expansion of 167×10⁻⁷ in/in/° C. and have goodchemical and electrical resistance.

    ______________________________________                                        Oxide         Molar %  Weight %                                               ______________________________________                                        SiO.sub.2     58.5     44.81                                                  Na.sub.2 O    13.0     10.27                                                  K.sub.2 O     13.0     15.61                                                  BaO           14.0     27.36                                                  Al.sub.2 O.sub.3                                                                            1.5      1.95                                                   ______________________________________                                    

The glass has a sealing temperature of about 750° C. which isparticularly suited for the manufacture of "window frame" packages asdescribed hereinbelow.

FIG. 1 illustrates in cross section a hermetic metal package 10 adaptedto house an electronic device 12, usually a silicon based semiconductor.Hermetic metal packages are disclosed in U.S. Pat. No. 4,524,238 to Buttand U.S. Pat. No. 4,656,499 to Butt and both are hereby incorporated byreference in the present application.

The package 10 is comprised of a base component 14, a window frame 16and a cover component 18. A leadframe 20 is disposed between the windowframe 16 and base component 14 and serves to electrically connect theelectronic device 12 to external circuitry.

While copper or a copper alloy may be used to manufacture the packagecomponents, copper alloys which form refractory oxides such as copperalloys C6381, C724 and C7025 are preferred for their glass sealingcapabilities. These and other copper alloys which form a surfacerefractory oxide when heated in an oxidizing atmosphere are referred toherein as alloys which form a glass sealable layer "in situ".

Other copper alloys may be coated with a glass sealable oxide formingmetal or metal alloy by cladding as disclosed in the above U.S. Pat. No.4,524,238 to Butt. Plating, vapor deposition or sputtering as disclosedin U.S. Pat. No. 796.083, entitled "SEMICONDUCTOR CASING", filed on July2, 1987, by Cherukuri et al. may also be used to deposit a materialwhich forms a refractory or glass sealable oxide onto the surface of thepackage components. This process is referred to herein as forming aglass sealable layer by an "additive" process.

Alloy 6381 contains 2.5-3.1% aluminum 1.5-2.1% silicon and the balancecopper as described in U.S. Pat. Nos. 3,341,369 and 3,475,227 issued toCaule et al. A refractory oxide layer formed substantially of aluminumoxide (Al₂ O₃) may be produced by any desired method. For example, thealloy may be preoxidized by heating to a temperature of between about330° C. and 820° C. in gases having an extremely low oxygen content suchas 4% hydrogen, 96% nitrogen and a trace of water.

Alloy C6381 may not be preferred for all packaging applications. Thealloy anneals at glass sealing temperatures and the assembled package issubject to distortion and damage due to its softened state. A morepreferred alloy would be a precipitation hardened alloy suitable forglass sealing such as copper alloy C724.

Alloy C724 consists essentially of from about 10% to about 15% nickel,from about 1% to about 3% aluminum, up to about 1% manganese, from about0.05% to less than about 0.5% magnesium and the balance copper asdisclosed in U.S. Pat. No. 4,434,016 to Saleh et al.

The use of alloy C724 as well as other precipitation hardened alloys forleadframes in glass sealed metal packages is disclosed in U.S. Pat. No.4,704,626 to Mahulikar which is hereby incorporated by reference in thepresent application.

Another preferred copper based alloy, C7025, consists essentially offrom about 2 to about 4.8 weight percent nickel, from about 0.2 to about1.4 weight percent silicon, from about 0.05 to about 0.45 weight percentmagnesium and the balance copper. Alloy C7025 is disclosed in U.S. Pat.No. 4,594,221 to Caron et al. Alloy C7025 achieves maximum hardness whenaged at a temperature of about 450° C. for about 2 hours.

The aging properties of precipitation hardenable copper alloys has beenexploited in glass sealed metal packages. U.S. Patent Application Ser.No. 2,532, entitled "PROCESS FOR PRODUCING FORMABLE AND HIGH STRENGTHLEADFRAMES FOR SEMICONDUCTOR PACKAGES", filed on Jan. 12, 1987, byMahulikar et al. teaches a process of providing a leadframe formed froma precipitation hardenable copper alloy in the homogeneous or softenedstate, bending the leadframe to shape, and then glass sealing thepackage using a glass which seals at about the age hardening temperatureof the leadframe alloy so that the alloy is age hardened during glasssealing.

Precipitation hardenable alloys are referred to as being in the solutiontreated or homogeneous state when they are single phase. These alloysare rather ductile. When the alloys are in the precipitation or agehardened state, they are multi-phase. These alloys are less ductile. Bycontrolled heating and cooling, an alloy may be transferred fromsolution treated to age hardened or from age hardened to solutiontreated.

An advantage of the glass of the present invention is it softens attemperatures above 700° C. so that a precipitation hardenable leadframemay be glass sealed in the solution treated state, bent to a desiredshape, and then age hardened without the properties of the glass beingdegraded.

Nothing in the above is intended to limit the package components toprecipitation hardened alloys or to a single alloy. For example, thebase component 14 may be comprised of oxygen free (OFHC) copper or ahigh conductivity copper alloy such as alloy C194 (1.5%-3.5% iron andsmall amounts of zinc or mixtures of zinc and phosphorous and thebalance copper as disclosed in U.S. Pat. No. 3,522,039 to McLain) oralloy C197 (0.3%-1.6% iron, 0.01%-0.20% magnesium, 0.10%-0.40%phosphorous, up to 0.5% tin or antimony or mixtures thereof and thebalance copper as disclosed in U.S. Pat. No. 4,605,532 to Knorr et al.)to facilitate the removal of heat from the electronic device. Theleadframe 20, the window frame 16 and the cover component 18 may beformed from a precipitation hardenable alloy to give the package 10extra strength. Any desired combination of materials could be employed.

Referring back to FIG. 1, an illustrative example of a glass sealedmetal package 10 in accordance with the present invention isillustrated. A base component 1, 4 is preferably formed from a highconductivity alloy such as C194 or C197 containing a glass sealablelayer 22 on at least a first surface 15 and, preferably, the edges ofthe package as well. The glass sealable layer is preferably a metaloxide or refractory oxide layer and may be applied by cladding. Forexample, cladding a layer of alloy C6381 on the surface of the basecomponent. Other additive processes such as plating, sputtering or vapordeposition may also be used. If cladding is utilized, the clad is oftenseveral mils thick and it may be desirable to remove the cladding fromthat portion of the base component which will bond to the chip 12 toincrease thermal conductivity. If plating, sputtering or vapordeposition is used, the refractory layer may be formed from nickel,silicon or other materials as disclosed in U.S. Pat. No. 4,796,083. Thecoating is generally much thinner and it is usually not necessary toremove the coating form the bonding site. The refractory layer 2, 2 isthen oxidized to form a refractory oxide 24 on the bonding surface ofthe refractory layer. A sealing glass 26 with a composition inaccordance with the present invention is applied to the refractory oxideby any applicable technique, for example, screening.

A similar process provides a window frame 16 with a refractory oxide 28on at least one surface. As the window frame does not contributesignificantly to the thermal dissipation of the package and is useful toincrease the strength of the package, the window frame is preferably aprecipitation hardened alloy which is capable of forming a refractoryoxide such as C724 or C7025. A glass 26 with a composition in accordancewith the present invention is applied to the refractory oxide layer 28of the window frame 16.

A leadframe 20, preferably formed from a precipitation hardenable alloyfor strength, although a high conductivity copper alloy such as C194 orC197 may be used, is disposed between the base component and the windowframe in contact with the two layers of sealing glass 26. To improve theglass to metal bond, it is often desirable to supply a refractory oxidelayer to first 19 and second 21 sides of the leadframe 20.

The assembly is then fired in a furnace at a temperature of about 700°C. to about 800° C. and, more preferably, at a temperature of from about740° C. to about 760° C. for a time of about 10 minutes to about 60minutes and, preferably, of about 25 to about 35 minutes. The furnaceatmosphere may be neutral or oxidizing, generally dependent on thecomposition of the package components. If the components arepreoxidized, a neutral or reducing atmosphere, such as 4% H₂, 96% N₂ maybe used. If the components are not preoxidized, a slightly oxidizingatmosphere, such as air or nitrogen with a trace of water may be used.

After sealing, the leadframe is in the solution treated state and thelead end portions 30 of the leadframe 20 may be bent to a desired radius32 without damaging the glass. The glass is then preferably annealed toremove residual stresses which may develop during sealing. Annealing attemperatures of from about 400° C. to about 500° C. is exemplary whiletemperatures from about 400° C. to about 450° C. are preferred and about430° C. is most preferred. The annealing time is up to about 2 hoursand, preferably, from about 20 minutes to about 1 hour and, mostpreferably, about 25 to about 35 minutes. It is an advantage of theglass of the present invention that the annealing temperature of theglass matches the age hardening temperature range for the desiredprecipitation hardenable copper alloys. While the glass is annealed, thecopper alloy hardens producing an electronic package of superiorstrength.

An electronic device 12 is next bonded to the base component by anyknown die attach system. The glass is not deteriorated by die attachtemperatures so any suitable material may be used for the die attach 34.This is a distinct advantage over previously known glasses which maydegrade at temperatures in excess of about 350° C. The electronic device12 is then electrically connected to lead fingers 35 by a known processsuch as wire bonding 36.

The cover component 18 is then attached to the second side of the windowframe 16 by a suitable bonding component 38. The sealing glass isthermally stable at temperatures of up to about 700° C., so the bondingcomponent 38 is selected to have a melting temperature low enough toavoid damage to the electronic device and softening of the precipitationhardened copper alloys. It is preferable to select a bonding componentwhich seals at temperatures less than about 400° C. Most conventionalCERDIP bonding components, for example, low temperature solder glassesor alloys such as 80% by weight gold and 20% by weight tin or lead-tinalloys are acceptable.

The second surface 40 of the window frame and the cover component 18 aresupplied with a refractory oxide, if a solder glass is used as thebonding component 38. If a metallic component is used, it is preferableto have the second surface 40 and cover component 18 bare metal orplated with a metal such as gold or tin to enhance solder wettability.

The package containing the window frame and cover component with asuitable bonding component disposed therebetween is heated to seal thecover component to the package, thereby completing the hermetic package10 in accordance with the present invention.

The present invention is not limited to hermetic metal packages asdescribed above. The sealing glass may be used in combination with ametal or any metal alloy where an approximate match in coefficients ofthermal expansion is desired.

Referring to FIG. 2, a glass-metal composite 50 is shown in crosssection.

The composite is comprised of a metal substrate 52 and a glass layer 54.Generally, a glass sealable layer 56 is disposed between the metalsubstrate and the glass layer. The glass sealable layer may be a metaloxide or a refractory oxide as described hereinabove and may be appliedby the techniques described above.

The composite may be used to fabricate a circuit assembly such as aprinted circuit board or a chip carrier. A circuit assembly is disclosedin U.S. Pat. No. 4,491,622 to Butt. A metal foil layer 58 may be bondedto the glass as disclosed in U.S. Pat. No. 4,712,161 to Pryor et al.Since the glass has a coefficient of thermal expansion approximatelyequal to that of copper, a copper or copper alloy substrate may be usedto take advantage of the high thermal conductivity of the copper.

As shown in FIG. 3, the sealing glass of the present invention may beused as a bonding glass for multi-layer circuits. A multi-layer circuitboard 60 is comprised of first 62 and second 64 substrates. Thesubstrates are any metal or metal alloy with a coefficient of thermalexpansion in excess of 160×10⁻⁷ in/in/° C. and, preferably, copper or acopper alloy. The bonding glass 66 is applied to at least one surface ofeach substrate as disclosed above and a layer of copper foil 68 is alsoadded. It may be desirable to provide glass sealable layers 70 to thesubstrate and foil to facilitate glass sealing. The substrates are thenstacked and bonded together.

The copper foil layers 68 are formed into circuit patterns, for example,by selectively applying a resist and then chemically etching away theuncovered portions of foil. Insulated conductive through-holes 72 mayalso be provided to supply electrical contact from one foil layer to thenext.

Since the coefficient of thermal expansion of the glass, substrates andfoil layers closely match, the multi-layer circuit is not limited to twolayers as shown in FIG. 3. Any number of substrates and foil layers maybe used with through-hole supplying electrical interconnection.

The composite is also useful as a decorative laminate. The glass limitsoxidation and corrosion of the underlying substrate. Examples ofdecorative composite material formed from a metallic substrate and aglass layer may be found in U.S. Pat. Nos. 3,826,627 and 3,826,629 bothto Pryor et al. The laminate is useful for plumbing fixtures, bathroomfixtures or jewelry or other uses for an enameled metal. The coefficientof thermal expansion of a composite manufactured according to thepresent invention is close to that of copper or a copper alloy. Anyapplication requiring enameled copper could preferably be made using thepresent glass and a copper or copper alloy substrate.

The advantages of a glass with a coefficient of thermal expansion whichmatches that of copper or a copper based alloy is not limited toelectronic and decorative applications. Any place a matched seal betweenglass and a high expansion alloy is required would benefit from the useof the glass of the present invention.

A useful applications would be matched glass to metal seals in vacuumdevices. These devices may be used for electrical devices such asdisclosed in U.S. Pat. No. 2,446,277 to Gordon or a pressurized vesselrequiring glass to metal seals such as a chemical reaction chamber oreven a submarine. The vessel need not be under vacuum, it may bepressurized or at atmospheric pressure.

The patents and patent applications set forth in this application areintended to be incorporated in their entireties by reference herein.

It is apparent there has been provided in accordance with this inventiona sealing glass suitable for the assembly of hermetic metal packages andthe packages so produced which satisfy the objects means and advantagesset forth hereinabove. While the invention has been described incombination with the embodiments thereof, it is evident that manyalternatives, modifications and variations will be apparent to thoseskilled in the art in light of the foregoing description. Accordingly,it is intended to embrace all such alternatives, modifications andvariations as fall within the spirit and broad scope of the appendedclaims.

What is claimed is:
 1. A metal-glass composite, comprising:a first metalor metal alloy component; a glass sealable layer on at least one surfaceof said metal or metal alloy; and a sealing glass component bonded tosaid metal or metal alloy component by means of said sealable layer,said glass sealing component consisting essentially of at least 50 molarpercent SiO₂, from about 12 to about 15 molar percent BaO such that saidsealing glass component has a coefficient of thermal expansion of fromabout 165×10⁻⁷ in/in/° C. to about 175×10⁻⁷ in/in/° C., from abouttwenty to about thirty molar percent of an alkaline oxide component,said alkaline oxide component comprised of at least two alkaline oxidesselected from the group consisting of Na₂ O, K₂ O and Li₂ O; from about0.5 molar percent to about five molar percent Al₂ O₃ ; and up to about10 molar percent of an additive selected from the group consisting of B₂O₃₂ P₂ O₅, MgO, CaO, GeO2, SrO, PbO and mixtures thereof.
 2. Thecomposite of claim 1 wherein said substrate is copper or a copper basedalloy.
 3. The composite of claim 2 wherein the concentration of SiO₂within said glass component is in the range of from about fifty-fivemolar percent to about sixty-five molar percent.
 4. The composite ofclaim 3 wherein the concentration of SiO₂ within said glass component isfrom about fifty eight molar percent to about sixty molar percent. 5.The composite of claim 4 wherein the concentration of BaO in said glasscomponent is selected so that said glass has a coefficient of thermalexpansion approximately equal to that of said first metal or metalalloy.
 6. The composite of claim 5 wherein said at least two alkalineoxides are present in essentially equal molar concentrations.
 7. Thecomposite of claim 6 wherein said alkaline oxide component consists ofessentially equal molar concentrations of Na₂ O and Li₂ O.
 8. Thecomposite of claim 1 wherein said concentration of Al₂ O₃ in said glassis in the range of from about 0.5 molar percent to about 3 molarpercent.